Pitcher plant description

The tropical pitcher plants of Asia (Nepenthes species) are amongst the largest and most spectacular of all carnivorous plants. Nepenthes aristolochioides is a vine that climbs to a height of about five metres and has modified pitcher-shaped leaves hanging from long, coiled tendrils (2). Nepenthes species usually have two or three different types of pitcher, generally known as upper and lower pitchers (4). In Nepenthes aristolochiodes, the trumpet-shaped pitchers are greenish-white with red speckles, with the mouth situated uniquely at the front of the pitcher (2). Insects and other invertebrates fall into the pitchers, which contain an acidic fluid, secreted by the many glands that cover the inside surface of the lower half of the pitcher (4). The smooth and waxy upper inner surface of the pitcher makes it impossible for captive insects to gain a foothold (4), and a ridge of hardened tissue lining the mouth of the pitcher, the peristome, bears downward pointing teeth, also preventing insects from escaping. A deep red lid overhanging the mouth of the pitcher prevents rain water from diluting the pitcher fluid (2)(5). The pitchers, leaf axils and leaf midribs are covered with white, flat hairs, while the rest of the plant is hairless (2)(6)

Related species

Pitcher plant biology

Pitcher plants are dioecious meaning that male and female flowers grow on separate plants (4), and only begin to flower once the upper pitchers are produced (6). The flowers produce large amounts of nectar during the early evening and night, which evaporates by the morning. This nectar attracts flies during the early evening and moths at night to aid pollination. Once fertilised, a fruit usually takes about three months to develop and ripen. The fruits of Nepenthes species produce between 100 and 500 very light, winged seeds, which can measure up to 30 millimetres long, and are thought to be dispersed by the wind (2)(5). Despite enormous numbers of seeds being produced, only a few manage to germinate and only a fraction of those survive to maturity (5).

Carnivorous pitcher plants are adapted to grow in soils low in nutrients. Although the plants do gain some nutrition through the soil, and energy through photosynthesis, they supplement this with a diet of invertebrates, usually consisting of ants, cockroaches, centipedes, flies and beetles. Insects are attracted to the pitchers by their bright colours and nectar, which is secreted by glands situated on the lid and the peristome of the pitcher. The insects fall into the acidic fluid at the base of the pitcher and, unable to escape, they drown. Digestive enzymes are then released to break down the captured prey (4).

Despite the hostile environment of the pitchers, they can be home to number of animals. The red crab spider (Misumenops nepenthicola) inhabits pitcher plants in Malaysia, Indonesia and Singapore. This spider ambushes insects that crawl into the pitcher, and preys upon other insects, such as mosquitoes, as they emerge from larvae that live in the pitcher fluid (5).

Pitcher plant status

Pitcher plant threats

Nepenthes species are threatened by a combination of over-collection and habitat loss (5). Nepenthes aristolochoides is particularly threatened by over-collection and recovery is hampered by its extremely restricted range, as it grows only on Mount Kerici. Species that have a highly restricted range are particularly susceptible to extinction if habitats are disturbed or from catastrophic environmental events, such as drought and fire. In addition, highland plants, such as Nepenthes aristolochoides,take longer to recover than lowland plants as growth is slower (2).

Pitcher plant conservation

Nepenthes aristolochiodes is found within Kerinci-seblat National Park, but over-collection and habitat loss remains a problem (2). Although listed under Appendix II on the Convention on International Trade in Endangered Species (CITES), which limits the international export of this species (3), trade is very difficult to regulate. There is no requirement for internationally traded Nepenthes to be identified down to species level and plants simply labelled as Nepenthes accounted for 94 percent of all exported Nepenthes plants between 1988 and 1993. This needs to be remedied and urgent attention is required to close other trade loopholes (5). Nepenthes aristolochioides is being cultivated, helping to reduce the impact on wild populations (5).

Authentication

Glossary

The angle between the upper side of a leaf or stem and the supporting stem or branch.

Carnivore

Flesh-eating.

Endemic

A species or taxonomic group that is only found in one particular country or geographic area.

Enzymes

Proteins that trigger, or accelerate, activity in the cells of the body, for example, breaking down foods during digestion, and building new proteins..

Epiphyte

A plant that uses another plant, typically a tree, for its physical support, but which does not draw nourishment from it.

Fertilisation

In a flowering plant, fertilisation is the process of a pollen grain joining with the ovule (female egg cell). After fertilisation, the female parts of the flower develop into a fruit.

Invertebrates

Animals with no backbone.

Larvae

Stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.

Midrib

The vein in the centre of a leaf.

Photosynthesis

Metabolic process characteristic of plants in which carbon dioxide is broken down, using energy from sunlight absorbed by the green pigment chlorophyll. Organic compounds are made and oxygen is given off as a by-product.

Pollination

The transfer of pollen grains from the stamen (male part of a flower) to the stigma (female part of a flower) of a flowering plant. This usually leads to fertilisation, the development of seeds and, eventually, a new plant.

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